This is a revised competitive renewal proposal for the Training Program entitled: Training in Pediatric Gastroenterology and Nutrition. The overarching goal of the Training Program (entering its 30th year) is to prepare MD, MD/PhD pediatricians, and PhD basic scientists for careers in independent research on topics relevant to digestive diseases in infancy, childhood, and adult life. We offer training in 4 broad areas of Basic and Clinical/Translational science relevant to the Digestive Diseases: * Epithelial/Neuro-endocrine Cell Biology/Physiology & Stem Cell and Developmental Biology; * Innate and Adaptive Mucosal Immunology; * Microbiology, Microbial Pathogenesis, and the Gut Microbiome; and * Clinical/Translational research. The program provides an in depth comprehensive scientific experience for each trainee in a research group at the forefront of its field. Seven postdoctoral positions are requested for 2-3 years of research training. 60 core reseach faculty support this effort. Training faculty are drawn from all Harvard Affiliated Hospitals and Research Institutes, the Harvard Medical School, and the Harvard School of Public Health. Opportunities for cross-fertilization are abundant. The Program Director is Dr. Wayne I. Lencer MD, Professor of Pediatrics, Harvard Medical School, a widely respected investigator and mentor. Dr. Scott Snapper MD PhD, Associate Professor HMS and highly accomplished investigator will act as co-director for the pre-doctoral program in mucosal immunology. A Mentoring Program and Scholarship Oversight Committee (SOC) or Dissertation Advisory Committee (DAC), led by Drs. Lencer, Snapper, and two accomplished and well respected previously NIH-funded HMS Professors (Marian Neutra PhD and Richard Grand MD), are assembled for each trainee to provide mentoring and oversight in scientific and career development. Didactic course work is required for both basic and clinical research training tracks and supplemented with relevant seminars and journal clubs, a course in the responsible conduct of research, and an annual research retreat. Trainees in clinical research must obtain a Master's Degree in Medical Science or Public Heath (MMSc or MPH) from the Harvard Medical School or Harvard School of Public Health. Integration of training with the candidates' future goals in academic medicine, a strong focus on original research, and strong mentoring in science and career development are essential features of the program.